Both sides had struggled to create chances throughout the encounter, but Fletcher and Gielnik got on the scoresheet as the game opened up in the second half.
The visitors had the better of the play in the first half, and hit the crossbar in just the third minute.
Catherine Canulli whipped in a cross from the left, and Tameka Butt - under fierce pressure from Victory defender Maika Ruyter-Hooley - poked her shot onto the bar.
Neither team was able to create any further clear-cut opportunities in the first half, forced to try their lucks from distance.
While there were just two shots on target in the opening 45, the game began to open up in warm conditions after the restart.
Roar attacker Joanne Burgess flashed a volley just wide early in the second half, before Victory captain Jodie Taylor became influential.
Taylor, who has scored seven times this campaign, had a shot well-saved by Roar goalkeeper Casey Dumont on 57 minutes.
The prolific forward then had an excellent chance to open the scoring just after the hour-mark.
Played through by Katrina Gorry, who she combined with well throughout, Taylor forced another save from Dumont in a one-on-one.
Butt went within inches of putting the champions ahead in the 72nd minute, but, after a pass from Gielnik, her first-time effort from 20 yards went just wide of Brianna Davey's left post.
Victory would find the opener 12 minutes from time when Fletcher struck.
Ashley Brown lofted a corner to the back post, and Fletcher rose highest to nod in her second goal of the season.
Yet, the Roar pushed hard for an equaliser and found it through substitute Gielnik in the first minute of additional time.
Captain Clare Polkinghorne was given space and time on the right, and she picked out the run of Gielnik, who beat Davey to the cross and side-footed in the dramatic late leveller.
Melbourne Victory 1 (Kendall Fletcher 79’)
Brisbane Roar 1 (Emily Gielnik 91’)
Saturday 17 December 2011
Simonds Stadium, Geelong
Referee: Kate Jacewicz / AR1: Laura Moya / AR2: Danielle Anderson / 4th Official: Catherine Hoffmann
Melbourne Victory: Brianna DAVEY (gk), Rebekah STOTT, Maika RUYTER-HOOLEY, Kendall FLETCHER, Danielle JOHNSON, Stephanie CATLEY, Ashley BROWN, Jodie TAYLOR, Catlin FRIEND (Enza BARILLA 70’), Katrina GORRY (Georgie KOUTROVELIS 86’), Amy JACKSON
Substitutes not used: Cassandra DIMOVSKI (gk), Rita MANKOWSKA
Yellow Cards: Gorry 29’ Ruyter-Hooley 65’
Red Cards: Nil
Brisbane Roar: Casey DUMONT (gk), Laura ALLEWAY, Clare POLKINGHORNE, Brooke SPENCE, Joanne BURGESS, Kim CARROLL, Catherine CANNULI (Emily GIELNIK 67’), Lana HARCH, Aivi LUIK, Tameka BUTT, Vedrana POPOVIC (Olga CEBRIAN-GARCIA 84’)
Substitutes not used: Hoshimi KISHI (gk), Ellen BEAUMONT
Yellow cards: Nil
Red cards: Nil